Our aim is to determine if active muscle blood flow during graded dynamic leg exercise is influenced by primary aging, gender or chronic physical activity. We will test the hypothesis that leg blood flow (femoral vein thermodilution) and conductance at any given submaximal cycle ergometer power output and whole body VO2 is less in sedentary older men and women in comparison to their younger counterparts (i.e., young sedentary) and their endurance-trained peers (older athlete). We will also test the hypothesis that reduced leg muscle blood flow in sedentary aging is associated with reduced cardiac output, reduced leg muscle mass, and increased norepinphrine spiillover in the legs. Specifically, 1768-97, is focused on young, sedentary men and women. The protocol involves performance tests before and after approximately 3 months of exercise training on the bike or treadmill. To date, we have enrolled a total of 7 volunteers (5 females, 2 males) in this protocol. One male withdrew from the study (prior to the exercise training period), and one female has completed the entire protocol. Of the five remaining volunteers currently enrolled, 3 have completed the pre-testing visits. We are currently recruiting "control subjects" and plan to enroll them before the end of the year. Based on our preliminary findings, we anticipate that a total of 10 patients will be studied, including control subjects. We have IRB approval to study 15 patients if necessary. The anticipated end date for this protocol is June 1999.